Subqueries
command
A query nested inside another query. Can be used in SELECT, FROM, WHERE, and HAVING clauses.
Syntax
SELECT ... WHERE col IN (SELECT col FROM ...);
Example
sql
-- Users who placed at least one order
SELECT name FROM users
WHERE id IN (SELECT DISTINCT user_id FROM orders);
-- Products above average price
SELECT name, price FROM products
WHERE price > (SELECT AVG(price) FROM products);
-- Subquery in FROM
SELECT dept, avg_sal FROM
(SELECT department AS dept, AVG(salary) AS avg_sal FROM employees GROUP BY department) AS dept_avg
WHERE avg_sal > 50000;